In particular when the yarn is running, while the tensiometer measures the force imparted by the yarn, the bending element may be excited to oscillate. The oscillations might falsify the precise reading of the force or the yarn tension. The damping element secured to the bending element, for this reason, has to dampen the oscillations to a predetermined, desirable extent.
The tensiometer known from EP 0 475 001 A has a foam material strip glued to the side of the bending element in order to dampen oscillations of the bending element.
The tensiometer known from DE 90 00 443 U has a damping element made from fluor composition rubber which is secured to the bending element by a nipple engaging into a longitudinal slot of the bending element in order to adjust the position of the damping element in the longitudinal direction and to adjust the damping effect.
The tensiometer known from WO 2006/005518 A contains an elastomeric element glued to the bending arm and an oscillation-extinguishing mass glued to the free side of the elastomeric element.
The tensiometer known from WO 2004/039714 A has a massive pin protruding from the bending element. The pin engages into a stationary cylinder filled with low viscosity liquid.
Known tensiometers with a “massive”, unitary damping element made of rubber or elastomer material has an insufficient damping effect. Additionally, known tensiometers, having some means for obtaining the desirable damping effect, are usually very prone to collect lint or avivage (chemical substance added to the yarn).
A tensiometer for measuring the force imparted by a yarn to a bending element according to the invention includes a bending element secured in a fixation and deflectable by the yarn. The tensiometer includes a unitary oscillation-damping element made of an intrinsically damping material like rubber or an elastomer, and the damping element is secured to the bending element. The unitary damping element includes a base body secured to the bending element and an oscillation body which can oscillate at least essentially in the direction in which the bending element is deflected by the yarn in relation to the base body and to the bending element, and an energy dissipation zone is provided in the damping element between the oscillation body and the base body.
It is an object of the invention to provide a tensiometer of the kind as referred to above, which can be manufactured at low cost, is reliable and does not suffer from lint or avivage collection.
The unitary damping body, having at least one oscillation body, which can oscillate substantially in the direction in which the bending arm is deflected by the yarn, allows fine-tuning of the damping effect. Only the base body has to be secured at the bending element, e.g. by clamping or gluing. The oscillation body, when excited by oscillations of the bending arm, will oscillate in relation to the base body and the bending arm, causing energy dissipation in the energy dissipation zone. Hence, the oscillation body functions like an oscillation-extinguishing mass although the oscillation body is a unitary component of the damping element. The damping effect is excellent. The tensiometer is not prone to lint or avivage depositions. The damping effect is not only achieved by the energy dissipation in the energy dissipation zone, but also by a damping effect from the ambient air, because the oscillations of the oscillation body and in turn of the bending element also are damped in the ambient air. The tensiometer can be produced in a large volume for low cost and via a small number of assembly steps (less assembling-manpower needed).
In an expedient embodiment the oscillation body is freely ending “in the air”. This concept does not only allow a relatively unrestricted oscillation of the oscillation body, but also avoids lint or avivage depositions which could negatively influence the damping behaviour. Due to the oscillation of the oscillation body, contamination will be strongly repelled or “pushed away” from the oscillation body.
In an expedient embodiment the damping element has a U-shape. The first U-leg is secured to the bending element and constitutes the base body. The second U-leg is freely ending in the ambient air and constitutes the oscillation body. The U-bend constitutes the energy dissipation zone. The U-shaped damping element is a cheap component, e.g. a cut section of an extruded profile made of rubber or elastomer material. The fixation of the damping element only needs one gluing zone or one clamping zone.
Both U-legs of the U-shaped damping element may extend substantially in the longitudinal direction of the bending element. The second U-leg has a large unobstructed range for the oscillations and will be damped not only in the energy dissipation zone but also on both sides by the surrounding air. It is expedient to position the damping element as close as possible to the region of the bending element where the yarn contacts the bending element.
In another embodiment the damping element is an essentially L-shaped hook made e.g. from rubber or elastomer material. One L-end is secured to the bending element, while the other L-end extends essentially parallel and distant to the bending element.
In another embodiment an essentially S-shaped damping element is provided such that a first S-leg is secured to the bending element, while the second S-leg extends distant to the bending element. The remaining part of the S-shape constitutes the energy dissipation zone. The damping element also in this case may be a cut-off portion of an extruded “endless” profile.
In another embodiment a wear protector is placed where the yarn contacts the bending element. The wear protector can be used as a clamping element to secure the respective damping element at the bending element. This eliminates the necessity to provide a gluing fixation at all.
In another embodiment the damping element is shaped like a pot e.g. made of rubber or elastomer material. The rim of the pot is secured to the bending element, while the pot bottom constitutes the oscillation body. The outer wall of the pot constitutes the energy dissipation zone. This embodiment is advantageous because it is not at all prone to lint or avivage depositions. The pot bottom oscillates. Due to the rectangular or round shape of the pot a large energy dissipation zone is formed.
In order to enhance the damping behaviour a thickened portion may be formed in the pot bottom, which oscillates in relation to the bending element. Moreover, air enclosed in the pot might contribute to the damping effect.
Alternatively, the pot may be equipped with a venting hole communicating the interior of the pot with the ambient air. This might be advantageous with a view to achieving a reliable and constant damping behaviour.
In another embodiment the damping element has a Z-shape such that several oscillation bodies and several energy dissipation zones are constituted already by the shape of the damping element.
In another embodiment the base body either partially or entirely surrounds the bending element for securing the damping element to the bending element without the need of gluing.
In order to safeguard the position of the damping element on the bending element, at least one recess or projection could be provided on the bending element for positioning the base body of the bending element, which totally or partially surrounds the bending element.
The base body of this embodiment of the damping element may be either a ring or a C-shaped clip using the material elasticity for reliably positioning the damping element on the bending element. At least one ear-shaped tab or “wing” is protruding from the base body such that it extends lateral to the direction of the deflection of the bending element. This embodiment is particularly advantageous because it is nearly entirely insensitive to lint or avivage depositions, because there is no cavity where lint can be collected.
In another expedient embodiment two oppositely extending tabs or “wings” are formed on the base body such that the damping effect is obtained symmetrically with respect to the plane in which the bending element oscillates.